THE OLDEST KNOWN STROPHOMENOID FROM THE SANDAOKAN FORMATION (LATE ARENIG,ORDOVICIAN) OF INNER MONGOLIA,NORTH CHINA
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Abstract:
New material from the basal Sandaokan Formation (early late Arenig,Ordovician) of southern Inner Mongolia,North China represents a new species, Hesperinia sinensis, which is the oldest known strophomenoid brachiopods.It extends the record of this group into the Arenig,earlier than Llanvirn as generally known in the literature.Its cardinalia and some other crucial characters indicate that it is a strophomenid.The most important morphological transformations characterising the divergence of strophomenoids from ancestral plectambonitoids were the development of: a bilobed cardinal process, a pair of postero laterally curved socket ridges, and transmuscle ridges and side septa in the dorsal valve.These innovations are present in H.sinensis sp.nov.and confirm that the divergence of the strophomenoids from the plectambonitoids was pre late Arenig in age.Synecological analysis shows that Hesperinia sinensis sp.nov.occupied a near shore,shallow water,relatively high energy environment.
